1. Field of the Invention
The invention relates generally to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to air-ride axle/suspension systems for heavy-duty vehicles, which utilize an air spring to cushion the ride of the vehicle. More specifically, the invention is directed to a piston for an air spring of a heavy-duty vehicle air-ride axle/suspension system, in which the air spring piston upper portion is formed in two parts, including a top plate and a continuous stepped sidewall. Forming the top plate as a discrete part from the continuous stepped sidewall allows for more efficient manufacture of the air spring piston. A downwardly extending piston bottom plate allows for increased piston volume, which in turn provides a reduced spring rate, and/or better damping characteristics to the air spring.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members, which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger, which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The opposite end of each beam also is connected to an air spring, or its equivalent, which in turn is connected to a respective one of the main members. A height control valve is mounted on the hanger or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system and one or more shock absorbers for providing additional damping to the vehicle axle/suspension system are also included. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams, which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental affect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring, while a shock absorber typically provides additional damping to the axle/suspension system.
The typical air spring of the type utilized in heavy-duty air-ride axle/suspension systems includes three main components, a flexible bellows, a bellows top plate and a piston. The bellows is typically formed from rubber or other flexible material, and is sealingly engaged with the bellows top plate and also to the top portion of the piston. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows and, in some cases, the piston of the air spring. The larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it allows for softer ride characteristics for the vehicle. Typically, the piston either contains a hollow cavity, which is in communication with the bellows and which adds to the air volume of the air spring by allowing unrestricted communication of air between the piston and the bellows volumes, or the piston has a generally hollow cylindrical-shape and does not communicate with the bellows volume, whereby the piston does not contribute to the air volume of the air spring. The air volume of the air spring is in fluid communication with an air source, such as an air supply tank, and also is in fluid communication with the height control valve of the vehicle. The height control valve, by directing air flow into and out of the air spring of the axle/suspension system, helps maintain the desired ride height of the vehicle.
The prior art air spring piston is generally cylindrically shaped and includes a continuous generally stepped sidewall attached to a generally flat bottom plate. A top plate is formed at the top of the piston. The bottom plate is formed with an upwardly extending central hub. The central hub includes a bottom plate formed with one or more central openings. A fastener is disposed through the openings in the central hub bottom plate in order to attach the piston to the beam of the suspension assembly at its rear end. The top plate, sidewall and bottom plate of the piston define a piston chamber having an interior volume. The top plate of the piston is formed with a circular upwardly extending protrusion having a lip or barb around its circumference. The barb cooperates with the lowermost end of the air spring bellows to form an airtight seal between the bellows and the piston. A bumper is attached to a bumper mounting plate, which is in turn mounted on the piston top plate by a fastener. The bumper extends upwardly from the top surface of the bumper mounting plate and serves as a cushion between the piston top plate and the bellows top plate in order to cushion contact between the two plates during operation of the vehicle. The piston is typically formed from steel, aluminum, fiber reinforced plastic or other rigid material.
Because the prior art air spring piston typically has a relatively complex integral one-piece structural design, manufacture of the piston from composite materials can be complicated. More particularly, because the lip or barb is integrally formed in one piece on the upwardly extending protrusion, which in turn is integrally formed in one piece with the top plate of the piston, manufacture of the piston from composite materials can be quite complex and therefore inefficient, as is well known to those of ordinary skill in the art. In addition, because the bottom plates of the piston and the central hub, respectively, are generally flat, the volume contained in the piston is generally limited because of spatial limitations between the beam of the suspension assembly and the main member of the vehicle.
The air spring piston for heavy-duty vehicles of the present invention, overcomes the problems associated with prior art air spring piston designs by providing an air spring piston upper portion formed in two parts that are assembled. Moreover, the air spring piston for heavy-duty vehicles of the present invention includes a downwardly extending piston bottom plate that allows for an increased piston volume while still utilizing the same mount configuration and hardware existing in prior art designs. This downwardly extending piston bottom plate allows for an increased piston volume without the need for redesigned or additional mounting brackets and without changing the spatial measurements between the beam and the main member. Therefore, the air spring piston for heavy-duty vehicles of the present invention provides for more efficient and simple manufacture that reduces manufacturing costs and provides for an increased piston chamber volume using existing piston-to-beam mounting hardware, whereby the increased piston chamber volume provides a reduced spring rate and/or better damping characteristics to the air spring.